Exposure apparatus and method

ABSTRACT

An exposure method immerses, in liquid, a surface of an object to be exposed, and a surface of a projection optical system closest to the object, and projects a repetitive pattern formed on a mask via the projection optical system onto the object. The exposure method may direct exposure light having a wavelength λ through a projection optical system that is at least partially immersed in liquid and has a numerical aperture of n o ·sin θ NA  greater than 0.9 in order to transfer a pattern formed on a mask onto an object to be exposed, wherein n o  is a refractive index of the liquid, Δn is the fluctuation of the refractive index of the liquid, θ NA  is the largest angle common to the liquid and a resist material applied to the object to be exposed, and d is a thickness of the liquid in an optical-axis direction of the projection optical system which satisfies d≦(0.03λ) cos θ NA /Δn.

This application is a divisional of application Ser. No. 11/229,541,filed Sep. 20, 2005, now U.S. Pat. No. 7,046,337 incorporated byreference, which is a divisional of application Ser. No. 10/732,768,filed Dec. 9, 2003, now U.S. Pat. No. 6,992,750 B2, issued Jan. 31,2006.

This application claims the benefit of priority based on Japanese PatentApplication No. 2002-358764, filed on Dec. 10, 2002, which is herebyincorporated by reference herein in its entirety as if fully set forthherein.

BACKGROUND OF THE INVENTION

The present invention relates generally to an exposure method andapparatus used to fabricate various devices including semiconductorchips such as ICs and LSIs, display devices such as liquid crystalpanels, sensing devices such as magnetic heads, and image pick-updevices such as CCDs, as well as fine contact hole patterns used formicromechanics, and more particularly to a so-called immersion typeexposure method and apparatus that immerse, in liquid, a surface of anobject to be exposed, and a bottom surface of a projection opticalsystem closest to the object, and expose an object via the liquid.

Reduction projection exposure apparatus has been conventionally employedwhich use a projection optical system for projecting a circuit patternformed on a mask (reticle) onto a wafer, etc. and for transferring thecircuit pattern, in manufacturing such fine semiconductor devices assemiconductor memories and logic circuits in the photolithographytechnology.

The critical dimension transferable by the projection exposure apparatusis proportionate to a wavelength of light used for exposure, andinversely proportionate to the numerical aperture (“NA”) of theprojection optical system. The shorter the wavelength is, the better theresolution is. Smaller resolution has been demanded with a demand forfiner semiconductor devices. The exposure light is requested to move tosmall wavelength, and the projection optical system is expected toimprove resolution using higher NA. Because of the difficulty ofchanging the exposure wavelength, a projection optical system hasaccelerated an improvement of its NA; for example, a projection opticalsystem having NA=0.9 has been developed.

On the other hand, light sources for the exposure apparatus have changedfrom a KrF laser (with a wavelength of 248 nm) to an ArF laser (with awavelength of 193 nm). At present, an F₂ laser (with a wavelength of 157nm) and EUV (with a wavelength of 13.5 nm) have been developed as nextgeneration light sources.

In such a situation, immersion exposure has called attentions, asdisclosed in Japanese Patent Publication No. 10-303114, as a method thatuses ArF laser (with a wavelength of 193 nm) and F₂ laser (with awavelength of 157 nm) for improved resolution. The immersion exposureuses a liquid as a medium at a wafer side. It fills the space betweenthe projection optical system and a wafer, to promote a higher NA.Specifically, the projection optical system has a numerical aperture(“NA”) of n·sin θ, where “n” is a refractive index of the liquid, and NAcan increase up to “n”.

Influence of polarized light on imaging performance becomesnon-negligible as NA becomes higher and higher, because the imagingperformance becomes different according to polarization directions asthe light has a larger incident angle upon a wafer.

The performance for two-beam imaging is much more affected bypolarization than that for three-beam imaging. In the three-beam imagingthat forms an image through interference among three beams, i.e., the0th order beam and the ±1st order diffracted beams, an angle does notreach 90° between the 0th order beam and the 1st order diffracted beamand between the 0th order beam and the −1st order diffracted beam, whichform a basic frequency for imaging, and the influence of polarizationdoes not appear significantly. On the other hand, two-beam imagingincludes the interference between two 1st diffracted beams and thatbetween the 0th order light and one of the ±1st order diffracted beams.The influence of polarization on the imaging performance is seriousbecause two beams that form the basic frequency have large angles.

Moreover, in the immersion case, two-beam imaging can problematicallymeet a condition in that no image is formed at all in a certainpolarized light direction. This phenomenon has not occurred in aconventional non-immersion optical system. When two interfering beamsare supposed to form an image as shown in FIG. 16A, p-polarized beamswith a polarization direction on the paper surface do not interfere witheach other or do not contribute to imaging because they form an angle of90°. When two beams are in symmetry and form an angle of 90°, anincident angle is 45° and sin 45°32 0.7.

On the other hand, s-polarized beams shown in FIG. 16B have apolarization direction orthogonal to the paper surface and form an imagewith good contrast. This fact now defines a polarization direction thatforms an image with good contrast as an s-polarized component ors-polarized light. As discussed, the s-polarized light has apolarization direction orthogonal to the paper surface when two beamsinterfere with each other on the paper surface. The polarizationdirection has implications with a direction in which a pattern isformed. When an interference fringe is formed by two beams, a directionof s-polarized light accords with each longitudinal direction of aninterference fringe formed by two beams: An X direction is a directionof the s-polarized light in forming an interference pattern whose finestructure extends in the X direction. A Y direction is a direction ofthe s-polarized light in forming an interference pattern whose finestructure extends in the Y direction.

When two-beam interference is considered which forms an image throughinterference between two beams having angles of ±θ_(r) in resist, wheren_(o) is a refractive index of a medium between a projection opticalsystem and the wafer, θ_(o) is an angle in the medium, and n_(r) is arefractive index of the resist, Equation (1) below is established fromthe Snell's law:n _(r)·sin θ_(r) =n _(o)·sin θ_(o)  (1)

When the medium is the air, Equation (2) below is established sincen_(o)=1 and sin θ_(o)<1:n _(r)·sin θ_(r) =n _(o)·sin θ_(o)<1  (2)

In the case of ArF excimer laser, the resist typically has a refractiveindex n_(r)=1.7, and Equation (2) leads to sin θ_(r)<0.59. Thus, whenthe medium is the air, the angle θ_(r) in the resist never shows sinθ_(r)=0.7. The cross angle of 90° condition in resist, consequently,never occurs.

On the other hand, in the case of immersion where the medium is liquid,Equation (3) below is established. When the medium has a refractiveindex n_(o)=1.47:n _(r)·sin θ_(r) =n _(o)·sin θ_(o)<1.47  (3)

Since the resist usually has the refractive index n_(r)=1.7, sinθ_(r)<0.86. Thus, when the medium is liquid, θ_(r) can attain thecondition sin θ_(r)<0.7.

Again, a condition never meets sin θ_(r)<0.7 when the medium is the air,whereas a condition can meet sin θ_(r)<0.7 when the medium is liquid,whereby the p-polarized light does not interfere and the contrast fromthe p-polarized light becomes zero. When the illumination light isnon-polarized, only the s-polarized light, which is the half of theincident light, contributes to imaging. The p-polized light does notcontribute to the imaging, thus halving the contrast, and creating areduced contrast problem.

For example, in the case of ArF excimer laser, Equation (4) below isestablished when the medium is water and n_(o)=1.47:

$\begin{matrix}{{\sin\;\theta_{o}} = {{\frac{n_{r}}{n_{o}}\sin\;\theta_{r}} = {{\frac{1.7}{1.47}\sin\mspace{11mu} 45^{\circ}} = 0.81}}} & (4)\end{matrix}$

As a consequence, water as the medium causes a condition that providesno interference of p-polarized light when sin θ_(o)=0.81. Thus, thep-polarized light does not form an image when an incident angle in themedium approximately meets sin θ_(o)=0.8. This problem is inevitablesince an optical system for immersion is required to have super-high NA,which means much larger than 1.0. In this case, the angle in the mediummeets sin θ_(o)=0.8. Even in case of F₂ excimer laser, the similarrelationship is established when sin θ_(o) is approximately 0.8 sincethe medium has a refractive index of around 1.36 and the resist has arefractive index of 1.5 or higher.

It is known that increased refractive indices of the resist and liquidare effective to increase NA. The resist and liquid have differentrefractive indices according to their materials. As disclosed in U.S.Pat. No. 4,346,164, a small difference of refractive index between theresist and liquid is preferable, but, in the usual case, sinOr in theresist is slightly smaller than sin θ_(o) in the medium. The inventorshave discovered that since it is anticipated that the resist forexclusive use with the immersion will be developed, it is preferable toset sin θ_(o) in the medium in the exposure apparatus side to beapproximately equivalent with sin θ_(r) in the resist. Thus, thecondition that provides no interference of p-polarized light may beregarded as sin θ_(o)≈sin θ_(r)=0.7.

As discussed, the high NA projection optical system is necessary forfiner patterns, while the imaging performance deteriorates due to thep-polarization features of the high NA imaging beam. In some cases, thedesired pattern cannot be formed as is predicted by the simple scalartheory, which does not count the polarization effect.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an exemplified object of the present invention toprovide an immersion type exposure method and apparatus which preventdeteriorated imaging performance due to influence of polarization,maintain desired contrast, and form desired patterns.

An exposure method of one aspect according to the present invention thatimmerses, in liquid, a surface of an object to be exposed, and a surfaceof a projection optical system closest to the object, and projects apattern formed on a mask via the projection optical system onto theobject, forms on a pupil of the projection optical system an effectivelight source that emits, from an axis orthogonal to an optical axis ofthe projection optical system, light that is parallel to the extendingdirection of the pattern and has an incident angle θ in the liquid,wherein the light includes only s-polarized light in an area of anincident angle θ that satisfies 90°−θ_(NA)≦θ≦θ_(NA), where θ_(NA) is thelargest value of the incident angle θ.

An exposure method of another aspect according to the present inventionthat transfers a pattern formed on a mask onto an object to be exposedvia a projection optical system that is at least partially immersed inliquid and has a numerical aperture of n_(o)·sin θ_(NA), where n_(o) isa refractive index of the liquid, illuminates the resist so that, wherean X-axis is one of the extending direction of the pattern formed on themask and a direction orthogonal to X-direction, a Y-axis, and θ is anincident angle to the resist from the liquid, an area of an effectivelight source formed on a pupil of the projection optical systemcorresponds to the incident angle θ that satisfies 90°−θ_(NA≦θ≦θ) _(NA),has a linearly polarized component in a orthogonal direction both on theX-axis and Y-axis.

An exposure method of still another aspect according to the presentinvention that transfers a pattern formed on a mask onto an object to beexposed via a projection optical system that is at least partiallyimmersed in liquid irradiates only s-polarized light onto an area on aneffective light source formed on a pupil of the projection opticalsystem, on which area two imaging exposure beams generate an orthogonalstate.

The area may have a canoe shape formed by intersecting two circles, ashape by linearly cutting down part of a circle, a shape by linearlycutting down part of an annular shape, or a circular shape.

An exposure method of still another aspect according to the presentinvention transfers a pattern formed on a mask onto an object to beexposed via exposure light having a wavelength λ and a projectionoptical system that is at least partially immersed in liquid and has anumerical aperture of n_(o)·sin θ_(NA), where n_(o) is a refractiveindex of the liquid, wherein the liquid has a thickness d in anoptical-axis direction of the projection optical system which satisfiesd≦3000·λ·cos θ_(NA).

An exposure method of another aspect according to the present inventiontransfers a pattern formed on a mask onto an object to be exposed via aprojection optical system that is at least partially immersed in liquid,wherein a surface of the projection optical system closest to the objectcontacts the liquid and is protected from the liquid.

An exposure apparatus of another aspect according to the presentinvention for transferring a pattern formed on a mask onto an object tobe exposed includes a projection optical system that is at leastpartially immersed in liquid and has a numerical aperture of n_(o)·sinθ_(NA), where n_(o) is a refractive index of the liquid; and apolarization control part for controlling polarization on an area on apupil of said projection optical system which corresponds to a range ofan angle θ at which exposure light exits from the projection opticalsystem, the range satisfying 90°−θ_(NA)≦θ≦θ_(NA), where θ_(NA) is thelargest value of the incident angle θ.

An exposure apparatus for transferring a pattern formed on a mask ontoan object to be exposed includes a projection optical system that is atleast partially immersed in liquid, and a polarization control part forcontrolling a polarization on an area on a pupil of said projectionoptical system, on which area two imaging exposure beams generate anorthogonal state.

The polarization control part may set the polarization to onlys-polarized light. The polarization control part may include apolarization element arranged approximately conjugate to a pupil surfaceof the projection optical system. The polarization control part mayinclude an aperture stop arranged on a pupil surface of the projectionoptical system, wherein the aperture stop has an aperture shape that isa canoe shape formed by intersecting two circles. The polarizationcontrol part may include an aperture stop arranged on a pupil surface ofthe projection optical system, wherein the aperture stop has an apertureshape by linearly cutting down part of a circle. The polarizationcontrol part may include an aperture stop arranged on a pupil surface ofthe projection optical system, wherein the aperture stop has an apertureshape by linearly cutting down part of an annulus.

The polarization control part may include an aperture stop arranged on apupil surface of the projection optical system, wherein the aperturestop has a circular aperture shape. The polarization control part maymaintain contrast of about 0.7 through control.

An exposure apparatus of another aspect according to the presentinvention includes a projection optical system that transfers a patternformed on a mask onto an object to be exposed, said exposure apparatusimmersing, in liquid, a surface of the object, and a surface of theprojection optical system closest to the object, and satisfyingd≦3000·λ·cos θ_(o) where n_(o)·sin θ_(o) is a numerical aperture of theprojection optical system, n_(o) is a refractive index of the liquid, λ(nm) is a wavelength of light used for exposure, and d is a thickness ofthe liquid in an optical-axis direction of the projection opticalsystem. The exposure apparatus may further include a sputtered film,wherein the surface of the projection optical system closest to theobject contacts the liquid, and is located on a calcium fluoridesubstrate and covered with the sputtered film.

A device manufacture method includes the steps of exposing an objectusing the above exposure apparatus, and performing a predeterminedprocess for the exposed object. Claims for a device fabricating methodfor performing operations similar to that of the above exposureapparatus cover devices as intermediate and final products. Such devicesinclude semiconductor chips like an LSI and VLSI, CCDs, LCDs, magneticsensors, thin filmn magnetic heads, and the like.

Other objects and further features of the present invention will becomereadily apparent from the following description of the preferredembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an exposure apparatus of oneembodiment, according to the present invention.

FIG. 2 is a plane view showing several exemplary patterns formed on amask shown in FIG. 1.

FIG. 3 is a conceptual view for explaining effects of p-polarized lightand s-polarized light.

FIGS. 4A and 4B are effective light source distributions that definepolarizations to expose mask patterns shown in FIGS. 2A and 2B.

FIG. 5 is an effective light source distribution that definespolarization to expose a mask pattern shown in FIG. 2C.

FIG. 6 is a typical view for explaining a relationship between aneffective light source area and a polarization direction.

FIG. 7 is a typical view for explaining a relationship between aneffective light source area and a polarization direction.

FIG. 8 is a typical view showing one example of an effective lightsource shape suitable for use with the mask pattern shown in FIG. 2Awhen the mask includes only fine patterns.

FIG. 9 is a typical view showing one example of an effective lightsource shape for use with the mask pattern shown in FIG. 2C when themask includes only fine patterns.

FIG. 10 is a typical view showing one example of an effective lightsource shape for use with mask patterns that extend in variousdirections.

FIG. 11 is a graph showing a relationship between a pitch and contrastdepth in the mask pattern shown in FIG. 2C.

FIG. 12 is a graph showing a relationship between a pitch and contrastdepth in the mask pattern shown in FIG. 2A.

FIG. 13 is a schematic view for explaining fluctuations of a medium(liquid) shown in FIG. 1.

FIG. 14 is a flowchart for explaining a device manufacture method thatuses the instant exposure apparatus.

FIG. 15 is a detail flowchart of a wafer process as Step 4 shown in FIG.13.

FIG. 16 is a schematic view showing a relationship between imaging andpolarized light in immersion type exposure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of an exposure apparatus 100 of oneembodiment according to the present invention with reference to FIG. 1.Here, FIG. 1 is a schematic block diagram of the exposure apparatus 100.As shown in FIG. 1, the exposure apparatus includes an illuminationsection 110, a mask or reticle 130, a reticle stage 132, a projectionoptical system 140, a main control unit 150, a monitor and input device150, a wafer 170, a wafer stage 176, and a liquid 180 as a medium. Thus,the exposure apparatus 100 is an immersion type exposure apparatus thatpartially or entirely immerses the space between the bottom surface ofthe projection optical system 140 and the wafer 170 with the liquid 180,and exposes patterns formed on the mask 130 to the wafer 170 via theliquid 180. Although the exposure apparatus 100 of the instantembodiment is a step-and-scan manner projection exposure apparatus, thepresent invention is applicable to a step-and-repeat manner and otherexposure methods.

The illumination apparatus 100 illuminates the mask 130 on which acircuit pattern to be transferred is formed, and includes a light sourcesection and an illumination optical system.

The light source section includes laser 112 as a light source, and abeam shaping system 114. The laser 112 may be pulsed laser such as ArFexcimer laser with a wavelength of approximately 193 nm, KrF excimerlaser with a wavelength of approximately 248 nm, F₂ laser with awavelength of approximately 157 nm, etc. A kind of laser, the number oflaser units, and a type of light source section is not limited.

The beam shaping system 114 can use, for example, a beam expander, etc.,with a plurality of cylindrical lenses, and convert an aspect ratio ofthe size of the sectional shape of a parallel beam from the laser 112into a desired value (for example, by changing the sectional shape froma rectangle to a square), thus reshaping the beam shape to a desiredone. The beam shaping system 114 forms a beam that has a size anddivergent angle necessary for illuminating an optical integrator 118described later.

The illumination optical system is an optical system that illuminatesthe mask 130, and includes a condensing optical system 116, apolarization control part 117, an optical integrator 118, an aperturestop 120, a condenser lens 122, a deflecting mirror 124, a masking blade126, and an imaging lens 128 in this embodiment. The illuminationoptical system 120 can cope with various illumination modes, such asconventional illumination, annular illumination, quadrupoleillumination, etc.

The condensing optical system 116 includes a necessary optical elemnts,and efficiently introduces a beam with the desired shape into theoptical integrator 118. In some cases, 116 involves a zoom lens systemto control the shape and angular distribution of the incident beam to118.

The condensing optical system 116 further includes an exposure doseregulator that can change an exposure dose of illumination light for themask 130 per illumination. The exposure dose regulator is controlled bythe main control unit 150. The position for monitoring the dose can beplaced other place, for example, between the fly's eye lens 118 and thereticle 130.

A polarization control part 117 includes, for example, a polarizationelement arranged at an approximately conjugate to a pupil 142 of theprojection optical system 140. The polarization control part 117controls, as described later, a polarization in a predetermined regionof an effective light source formed on the pupil 142. The polarizationcontrol part 117 can include plural types of polarization elements thatare provided on a turret rotatable by an actuator (not shown), and themain control unit 150 may control driving of the actuator.

The optical integrator 118 makes uniform illumination light thatilluminates the mask 130, includes as a fly-eye lens in the instantembodiment for converting an angular distribution of incident light intoa positional distribution, thus exiting the light. The fly-eye lens isso maintained that its incident plane and its exit plane are in theFourier transformation relationship, and a multiplicity of rod lenses(or fine lens elements). However, the optical integrator 118 usable forthe present invention is not limited to the fly-eye lens, and caninclude an optical rod, a diffraction grating, a plural pairs ofcylindrical lens array plates that are arranged so that these pairs areorthogonal to each other, etc.

Right after the exit plane of the optical integrator 118 is provided theaperture stop 120 that has a fixed shape and diameter. The aperture stop120 is arranged at a position approximately conjugate to the effectivelight source on the pupil 142 of the projection optical system 140, asdescribed later, and the aperture shape of the aperture stop 120corresponds to the effective light source shape on the pupil 142 surfacein the projection optical system 140. The aperture shape of the aperturestop 120 defines a shape of the effective light source, as describedlater. As described later, various aperture stops can be switched sothat it is located on the optical path by a stop exchange mechanism (oractuator) 121 according to illumination conditions. A drive control unit151 controlled by the main control unit 150 controls the driving of theactuator 121. The aperture stop 120 may be integrated with thepolarization control part 117.

The condenser lens 122 collects all the beams that have exited from asecondary light source near the exit plane of the optical integrator 118and passed through the aperture stop 120. The beams are reflected by themirror 124, and uniformly illuminate or Koehler-illuminate the maskingblade 126.

The masking blade 126 includes plural movable light shielding plates,and has an approximately rectangular opening corresponding to the usablearea shape of the projection optical system 140. The light that haspassed through the opening of the masking blade 126 is used asillumination light for the mask. The masking blade 126 is a stop havingan automatically variable opening width, thus making a transfer areachangeable. The exposure apparatus 100 may further include a scan blade,with a structure similar to the above masking blade 126, which makes theexposure are changeable in the scanning direction. The scan blade isalso a stop having an automatically variable opening width, and isplaced at an optically approximately conjugate position to the surfaceof the mask 130. Thus, the exposure apparatus can use these two variableblades to set the dimensions of the transfer area in accordance with thedimensions of an exposure shot.

The imaging lens 128 transfers an aperture shape of the masking blade126 onto the reticle 130 to be illuminated, and projects a reduced imageof the reticle 130 onto the wafer 170 installed on the wafer chuck.

The mask 130 has a circuit pattern or a pattern to be transferred, andis supported and driven by a mask stage 132. Diffracted light emittedfrom the mask 130 passes the projection optical system 140, and then isprojected onto the wafer 170. The wafer 170 is an object to be exposed,and the resist is coated thereon. The mask 130 and the wafer 170 arelocated in an optically conjugate relationship. The exposure apparatusin this embodiment is a step-and-scan type exposure apparatus (i.e.,“scanner”), and therefore, scans the mask 130 and the wafer 170 totransfer a pattern on the mask 130 onto the wafer 170. When it is astep-and-repeat type exposure apparatus (i.e., “stepper”), the mask 130and the wafer 170 are kept stationary for exposure.

FIG. 2 shows an example of a mask pattern. FIG. 2A is a plane view of amask pattern that has a repetitive direction in X-axis direction, and isextended in Y-axis direction. FIG. 2B is a plane view of a mask patternthat has a repetitive direction in Y-axis direction, and is extended inX-axis direction. FIG. 2C is a plane view of a mask pattern that blendsthese patterns.

The mask 130 is not limited to a binary mask, and may be a phaseshifting mask. A pattern formed on the mask 130 may include linepatterns, such as gates, contact holes or other patterns.

The mask stage 132 supports the mask 130, and is connected to atransport mechanism (not shown). The mask stage 132 and the projectionoptical system 140 are installed on a lens barrel stool supported via adamper, for example, to a base frame placed on the floor. The mask stage132 can use any structure known in the art. The transport mechanism (notshown) is made up of a linear motor and the like, and drives the maskstage 132 in X-Y directions, thus moving the mask 130. The exposureapparatus 100 scans the mask 130 and the wafer 170 in a statesynchronized with the main control unit 150.

The projection optical system 140 serves to image the diffracted lightthat has generated by the patterns formed on the mask 130 onto the wafer170. The projection optical system 140 may use an optical system solelycomposed of a plurality of lens elements, an optical system comprised ofa plurality of lens elements and at least one concave mirror (acatadioptric optical system), an optical system comprised of a pluralityof lens elements and at least one diffractive optical element such as akinoform, and a full mirror type optical system, and so on. Anynecessary correction of the chromatic aberration is available through aplurality of lens units made from glass materials having differentdispersion values (Abbe values), or arrange a diffractive opticalelement such that it disperses in a direction opposite to that of thelens unit. Otherwise, the compensation of the chromatic aberration isdone with the narrowing of spectral width of the laser. Nowadays,line-narrowed MOPA laser is one of the main stream.

The main control unit 150 controls the driving of each component, andparticularly controls the illuminator based on the information inputinto the input device of the monitor and input device 152, informationfrom the illumination apparatus 110, and a program stored in a memory(not shown). More specifically, the main control unit 150 controls, asdescribed later, a shape of the effective light source formed on thepupil 142 of the projection optical system 140, and polarization.Control information and other information for the main control unit 150are indicated on the display of the monitor and input device 152.

The wafer 170 is replaced with a liquid crystal plate and another objectto be exposed in another embodiment. The photoresist 172 is coated on asubstrate 174.

The wafer 170 is supported by a wafer stage 176. The stage 176 may useany structure known in the art, and thus a detailed description of itsstructure and operations is omitted. For example, the stage 176 uses alinear motor to move the wafer 170 in X-Y directions. The mask 130 andwafer 170 are, for example, scanned synchronously, and the positions ofthe mask stage 132 and wafer stage 176 are monitored, for example, by alaser interferometer and the like, so that both are driven at a constantspeed ratio. The stage 176 is installed on a stage stool supported onthe floor and the like, for example, via a dumper.

The bottom surface of the projection optical system 140 closest to thewafer 170 is immersed in the liquid 180. The liquid 180 selects itsmaterial that has good transmittance to the wavelength of the exposurelight, does not contaminate the projection optical system 140, andmatches the resist process. The coating of the last element of theprojection optical system 140 protects the elemnt from the water.

A description will now be given of polarization control by the maincontrol unit 150. A description will now be given of an effect ofpolarization, with reference to FIG. 3. Here, FIGS. 3A and 3B aretypical views for defining s-polarized light and p-polarized light. Asshown in FIG. 3A, the s-polarized light is defined as light thatpolarizes in a direction perpendicular to the cross-sectional plane(paper surface) of the projection optical system 140, or the light thatpolarizes, as shown in FIG. 16B, perpendicular to a plane that includestwo imaging beams. The p-polarized light is defined as light thatpolarizes in a direction parallel to the cross-sectional plane(papersurface) of the projection optical system 140, or light that polarizes,as shown in FIG. 16A, parallel to the surface that includes two imagingbeams.

In other words, if we take the XYZ axis as the following definitiontemporarily, the s-polarized light polarizes in the Y-axis direction andthe p-polarized light polarizes in the X-axis direction, where theX-axis is set in a direction parallel to the surface that includes twoimaging beams or the paper surface, and the Y-axis direction is set in adirection orthogonal to the surface that includes two imaging beams orthe paper surface, and a Z-axis is set in a propagation direction of thelight. A fine structure in a fine pattern extends perpendicular to thepaper surface and is assigned to the s-polarized light.

The imaging performance with higher resolution requires the p-polarizedlight that reduces the imaging contrast to be eliminated and only thes-polarized light to be used. In other words, as shown in FIG. 2A, themask pattern that is long in the Y-axis direction should use s-polarizedlight for imaging, which has a polarization direction in the Y-axisdirection as shown by an arrow.

Whereas, as shown in FIG. 2B, the mask pattern that is long in theX-axis direction should use s-polarized light for imaging, which has apolarization direction in the X-axis direction as shown by an arrow.

The present embodiment attempts to assign only the s-polarized light toan area on the effective light source, which allows two beams to form anangle sin Φ=0.7, where Φ (deg) is half an angle between these twodiffracted beams for imaging a pattern in the liquid 180.

This area corresponds an area that satisfies 90°−θ_(NA≦θ≦θ) _(NA) on theeffective light source formed on the pupil 142, in case of two-beaminterference such as 0th order light and 1st order light or ±1st orderlight as in a Levenson type phase shift mask in one embodiment, where θis an angle of light in the liquid 180 and θ_(NA) is the largest anglein the liquid. Although it is the resist that requires two beams toactually avoid forming 90°, θ_(NA) may be regarded as the largest anglecommon to the liquid and resist because θ_(o) may be considered to bealmost equal to θ_(r) when the liquid has a refractive index close tothat of the resist. In an alternative embodiment, this area is locatedon the effective light source formed on the pupil 142, and allows twoimaging exposure beams to generate an orthogonal state.

While a description has discussed a relationship between the s-polarizedlight and a pattern direction, this may be converted into a pupilcoordinate of the effective light source as follows: In the effectivelight source of illumination light on the pupil 142 of the projectionoptical system 140, the s-polarized light has a polarization directionalong a tangential direction orthogonal to a radial line from a centerof the pupil 142. Indeed, the s-polarized light is determined by adirection of a pattern to be imaged. Since actual LSI patterns ofteninclude patterns in the X and Y directions, the s-polarized lightbasically has a polarization direction in the X or Y direction: Aneffective light source area that has a polarization direction in the Xdirection can exist in the area having a center along the Y-axis on thepupil 142 of the projection optical system 140. An effective lightsource area that has a polarization direction in the Y direction canexist in the symmetrical area having a center along the X-axis on thepupil of the projection optical system. When a 45° direction isincluded, one example includes four directions X, Y and ±45°.

As a result of further investigations of the above conditions, this isachieved by assigning s-polarized light to a component in theillumination light emitted at an angle θ into the liquid 180 in FIG.16C, which is expressed by the following equations in the projectionoptical system 140 which meets θ_(NA)≧45° or sin θ_(NA)≧0.7, whereθ_(NA) is the largest angle in the liquid:sin(90°−θ_(NA))≦sin θ≦sin θ_(NA)  (5)90°−θ_(NA)≦θ≦θ_(NA)  (6)

Referring now to FIG. 16C, θ in Equations (5) and (6) is an incidentangle to the resist. In other words, θ means the angle at which theexposure light forms relative to a perpendicular to the substratesurface. θ_(NA) is the largest incident angle of the exposure light as amaximum value of the incident angle θ.

The maximum radius σ_(MAX) of the effective light source is nowconsidered in view of an angle without considering a refractive index,where the radius of the effective light source that is a light sourcedistribution of the illumination optical system projected on the pupil142. The radius of the pupil 142 is regarded 1 for nomalization. Then,Equation (6) corresponds, when using σ, to an assignment of s-polarizedlight to a range expressed by Equation (7) below of the effective lightsource area:σ_(IN)=sin(90°−θ_(NA))/sin θ_(NA)≦σ≦σ_(MAX)  (7)where σ_(MAX) is a parameter corresponding to the outermost part in theset effective light source distribution, and σ_(MAX)·sin θ_(NA) is thelargest angle of the illumination light in the liquid 180.

Since an actual LSI pattern often possesses specific directionalproperty in the X and Y directions, the selection of the effective lightsource shape should be considered. FIGS. 4 and 5 show two-dimensionaldistributions of effective light sources when the directional propertyis considered. Here, FIG. 4A is an effective light source distributionthat defines polarization to expose the mask pattern shown in FIG. 2A.FIG. 4B is an effective light source distribution that definespolarization to expose the mask pattern shown in FIG. 2B. FIG. 5 is aneffective light source distribution that defines polarization to exposea mask pattern shown in FIG. 2C.

A description will now be given of a relationship between an area on theeffective light source and a polarization direction, with reference toFIGS. 6 and 7. A mask pattern parallel to the Y direction is consideredas shown in FIG. 2A. As shown in FIG. 6, in the conventional case, anormal effective light source has a light source within a radius σ onthe effective light source in the normalized coordinates, and has themixed polarization state in the X and Y directions, since nopolarization is considered.

The s-polarized light is assigned to a polarization direction in the Ydirection shown by an arrow in the imaging of the mask pattern shown inFIG. 2A. FIG. 7 shows a pupil 142 in the projection optical system 140,and whitens the effective light source area (≦σ_(MAX)). The light thatemits at an angle of θ₁ from the projection optical system 140 to theliquid 180 enters a position at sin θ₁/sin θ_(NA) on a normalizedcoordinate of the effective light source. The mask pattern shown in FIG.2A is a sufficiently fine pattern below 0.5 in terms of a k₁ factor(=R/(λ/NA)). Two black dots connected by a broken line in FIG. 7indicate a two-beam interference pair of 0th and −1st order lights or0th and +1st order lights. A distance between two black dots isexpressed as 1/(2k₁) in the normalized coordinate. The diffracted beamtravels in a direction orthogonal to a direction in which each finepattern extends.

The immersion allows, as discussed above, a pair of beams to form anangle that approximately meets sin Φ=0.7, whereby the p-polarized lightdoes not provide the contrast at all. Therefore, the image contrast canbe improved through the assigrunnet of the polarization direction to theY direction as the s-polarized light in the area that generates such apair. A hatching region indicates the area that has a polarizationdirection to be controlled according to the pattern. The hatching regionrequires conditions that one of the two black dots which indicate the0th order light is included in a white part indicative of the effectivelight source, and the other one indicative of the ±1st light is includedin the pupil. The hatching region is found using the condition that theboth ends of the segment, having the distance of 1/(2k₁) between a pairof black dots, exist in the pupil 142. In this case, two hatchingregions (FIG. 8A) have a canoe shape as a result of an intersection oftwo circles. The present embodiment is characterized in that the angle θin the liquid 180 meets the following condition with respect to aboundary along the X-axis:sin(90°−θ_(NA))≦sin θ≦σ_(MAX)·sin θ_(NA)  (8)where σ_(MAX) is a parameter corresponding to the outermost part in theeffective light source, and σ_(MAX)·sin θ_(NA) is the largest angle ofthe illumination light in the liquid.

In FIG. 7, a line outside the region is a circle with a radius of themaximum effective light source σ_(MAX) and a center at X=0. On the otherhand, the inside forms a circle with a radius of 1 and a center atX=−(σ_(IN)+1) where σ_(IN) is expressed in the following equation:σ_(IN)=sin(90°−θ_(NA))/sin θ_(NA)  (9)

In other words, the region to be assigned to the s-polarized light isdefined by an intersection between a circle with a center at X=0 and aradius of the maximum effective light source σ_(MAX) and a circle with acenter at X=±(σ_(IN)+1) and a radius of 1, although FIG. 7 shows onlyone circle with a center at X=−(θ_(IN)+1) and a radius of 1.

While Equation (8) defines an on-axis angular range only along theX-axis or the Y-axis, there are illumination beams those are not on theaxis but are obliquely incident to the projection optical system. Sincethe oblique light has an angular range of α≦θ≦θ_(NA), a minimum value αbecomes a function of Y.

A coordinate that provides a minimum angular value α is located on acircle with a center at X=X₁ or X=X₂, Y=0. From X₁=+(σ_(IN)+1) andX₂=−(σ_(IN)+1), a circle with a center at X=X₁ meets (X−X₁)²+Y²=1 andX=X₁±√(1−Y)². For X≦1, X=X₁−√(1−Y)². From α=tan⁻¹(Y/X) (0≦α≦45°),α=tan⁻¹(Y/X)=tan⁻¹(Y/(X₁−√(1−Y)²)). Thus, the XZ plane parallel to theX-axis but not along the X-axis has the following angular range:α≦θ≦θ_(NA) (0 ≦α≦45°), where α=tan⁻¹(Y/X)=tan⁻¹(Y/(X₁−√(1−Y)²),X₁=+(σ_(IN)+1) where σ_(IN) is calculated from Equation (9).

The range of σ from σ_(IN)=sin(90°−θ_(NA))/sin θ_(NA) to σ_(MAX) shouldbe assigned to be only the s-polarized light in the Y direction on the Xaxis.

On the other hand, illumination light that has a small incident angle θ₁in the immersion medium, which meets sin θ₁≦sin(90°−θ_(NA)) does notcontribute to the imaging of fine patterns, but contributes to theimaging rough patterns with small diffracted angles. In this case, thepolarization is less influential and polarization control does not needto be considered. Either the non-polarized light or polarized light canbe assigned to this area, and shows little difference.

The present embodiment is thus characterized in that polarization isconsidered only for the light that is incident upon the hatching regionin the effective light source. As shown in FIG. 4A, these hatchingregions are symmetrical with respect to the Y-axis, and have apolarization direction in the Y direction for the s-polarized light or atangential direction in a circle that defines a pupil 142 of theprojection optical system 140.

The mask pattern shown in FIG. 2B that is parallel to the X directionmatches, as shown in FIG. 4B, a shape shown in FIG. 4A that is rotatedby 90°, and the hatching regions are symmetrical with respect to theX-axis, and have a polarization direction in the X direction as thes-polarized light. A boundary on the Y-axis is given by Equation (8).The boundary condition is the same that was calculated with respect tothe X-axis.

A mixture of similarly fine mask patterns shown in FIG. 2C parallel tothe X-axis and the Y-axis may utilize, as shown in FIG. 5A, the hatchingregions symmetrical to the X-axis and Y-axis, and have a polarizationdirection for s-polarized light in the X and Y directions as tangentialdirections. Boundary points on the X-axis and Y-axis meet Equation (8).As θ_(NA) increases, an overlap between the s-polarized region in the Xdirection and the s-polarized region in the Y direction occurs. Suchoverlapping region can be set to a non-polarized area, as shown in FIG.5B, or have zero light intensity. As shown in FIG. 5C, the polarizationmay be divided with respect to the lines crossing the center asboundaries. A similar effect is available when the effective lightsource has a polarization-direction distribution, as shown in FIG. 5D.

Dipole illumination shown in FIG. 8A is suitable for the mask patternshown in FIG. 2A. The pattern is limited in the fine dimension andextends in one direction. The effective light source shown in FIG. 8Ameets Equation (8) on the X-axis. When 0th order light enters thehatching region, one of ±1st order light passes the pupil. The dipoleillumination is efficient for the pattern such as FIG. 2A. Only if thedipole illumination meets Equation (8) on the X-axis, various shapes areapplicable, such as a shape shown in FIG. 8B that cuts a circle by aline, a shape shown in FIG. 8D that partially cuts an annulus with line,and a circle shown in FIG. 8C. In FIG. 8, the hatching part is a lighttransmitting part whose polarization is controlled, and a gray part is alight shielding part.

While FIG. 5 shows an exemplary effective light source suitable for themask pattern shown in FIG. 2C that has fine patterns extending in pluraldirections, annular illumination shown in FIG. 9 is also applicable. InFIGS. 9A and 9B, polarizations of the hatching regions are controlled,and gray parts are light shielding parts. A white part in FIG. 9A is alight transmitting part. Outer and inner diameters in the annularillumination area set within a range that meets Equation (8) on theX-axis and Y-axis, and polarization direction is set to the illustratedtangential direction. Boundaries of polarization located at portions of±45° may be non-polarized. Alternatively, polarization directions in theX and Y directions may be replaced with each other here.

A pattern that mixes 45° directions oblique to the. X-axis and Y-axiscan assign the s-polarized light to an area that meets Equation (8)according to pattern directions as shown in FIG. 10. In this case, σrange in the 45° directions is the same as Equation (8) according to therotational symmetry.

It is difficult in an actual optical system to insert a polarizationelement into the projection optical system 140 due to problems of heataberration, etc. Accordingly, the present embodiment controlspolarization of a predetermined area of the effective light source priorto the reticle 130. For example, polarization control part 117 providedprior to the optical integrator 118 is used to control polarization. Theoptical integrator 118 includes a portion conjugate to the pupil 142 ofthe projection optical system 140. To control the polarization state atthe optical integrator 118 is preferable in order to simplify theoptical system. The aperture stop 120 adjusts the shape of the effectivelight source. The aperture stop 120 can control polarization.

The projection optical system 140, except for a special configuration,usually does not have directional property of. Therefore, theconventional non-immersion system has treated the illumination light ina non-polarized state. That the illumination light does not have aspecial state of p-polarized light and s-polarized light in the radiusσ(σ≦1) or smaller on the effective light source. In case of immersion,however, it is understood, when the frequency components of imaginglight are considered, that the polarization condition suitable forimaging patterns in the X or Y direction exists. This conditioncorresponds to the polarization property in the aforementionedtangential direction or s-polarization characteristic. The polarizationeffect provides a different degree of deterioration to low and highfrequency patterns by the contribution from the p-polarized light. Highfrequency patterns use the peripheral regions of the pupil only, andvery sensitive to the polarization effect. On the other hand, the lowfrequency patterns use all the area and are not be influence by thepolarization much.

It is thus unnecessary to consider the influence of polarized lightbecause of the small contrast reduction in low frequency componentsinside the pupil 142 of the projection optical system 140. An opticalsystem for imaging rough patterns can be designed without consideringpolarization effects, since the polarization state is less influentialon the resolution performance.

Therefore, the effective light source shapes shown in FIGS. 4, 5 and8–10 proposed by the present embodiment may assign any polarized lightto its area on the effective light source outside the hatching region.The hatching region must have tangential polarization. The number ofpattern directions determines the way of defining the area to beassigned to the s-polarized light, and Equation (8) determines theregion on the axis which has the direction orthogonal to the patternline direction. The selected regions must be symmetrical. In otherwords, when a pattern has one direction, two regions should be assignedto the s-polarized light as shown in FIG. 4; when a pattern has twodirections, four regions should be assigned to the s-polarized light asshown in FIG. 5; when a pattern has three or four directions, a regionshould be assigned to the s-polarized light has approximately an annularshape as shown in FIG. 10. The effective light source shapes shown inFIGS. 8 and 9 are suitable in order to improve fine resolving power fora pattern that does not includes a large pattern but includes only finepatterns. The way of selecting a region to be assigned to thes-polarized light is the same as FIGS. 4 and 5, but different from FIGS.4 and 5 in that the center part is light-shielded.

The present embodiment realizes the effective light source shapes shownin FIGS. 4, 5 and 8–10 by an aperture shape of the aperture stop 120.These effective light source shapes are embodied as shapes of lighttransmitting and shielding parts of the aperture stop 120. The presentembodiment arranges plural types of aperture stops having these pluraleffective light source shapes on a turret, so that the actuator 121 mayswitch them. Similarly, plural types of polarization elementscorresponding to aperture shapes of the aperture stops are arranged on aturret so that an actuator (not shown) can switch them. One aspect ofthe present invention also involves an illumination optical system andexposure apparatus, which have the aperture stop 120 and polarizationcontrol element. The exposure apparatus has various exposure modes whichcontrol both the shape and polarization of the effective source.

In the exposure operation, beams emitted from the laser 112 are reshapedinto a desired beam shape by the beam shaping system 114, and then enterthe illumination optical system. The condensing optical system 116guides the beams to the optical integrator 118 efficiently. At thattime, the exposure-amount regulator adjusts the exposure dose of theillumination light.

The main control unit 150 recognizes mask pattern information inresponse to an input by a user through the input device in the monitorand input device 152, or by reading, for example, a barcode formed onthe mask, and selects the aperture shape and the polarization state asthe illumination conditions suitable for the mask patterning by drivingthe actuator for the aperture stop 120 and the actuator (not shown) forthe polarization control part 117. For example, the main control unit150 sets the polarization state as shown in FIG. 4A for the mask patternshown in FIG. 2A.

The optical integrator 118 makes the illumination light uniform, and theaperture stop 120 sets a desired effective light source shape. Suchillumination light illuminates the mask 130 under optimal conditionsthrough the deflecting mirror 124, the masking blade 126 and imaginglens 128.

Beams that have passed the mask 130 are projected under a specificmagnification onto the plate 400 by the projection optical system 140.The exposure apparatus of a step-and-scan type would fix the lightsource 112 and the projection optical system 140, and synchronously scanthe mask 130 and wafer 170, then exposing the entire shot. The waferstage 176 is stepped to the next shot and the new scan operation isdone. By repeating this exposure scanning and stepping, many shots areexposed to the wafer 170. The exposure apparatus of a step-and-repeattype, the exposure operation is done while the mask 130 and the wafer170 in a stationary state, and the stepping operation follows.

Since the bottom surface of the projection optical system 140 closest tothe wafer 170 is immersed in the liquid 180 that has a higher refractiveindex than that of the air, the projection optical system 150 has ahigher NA, and finer resolution is achieved. In addition, thepolarization control forms an image with higher contrast on the resist172. As a result, the exposure apparatus 100 can perform a precisepattern transfer onto the resist, can provide high-quality devices (suchas semiconductor devices, LCD devices, photographing devices (such asCCDs, etc.), thin film magnetic heads, and the like).

EXAMPLE 1

A description will be given of an example 1 according to the presentinvention utilizing the immersion type exposure apparatus 100. Theexposure apparatus 100 uses ArF excimer laser (with a wavelength of 193nm) as the light source 112, and projection optical system 140 having anumerical aperture of 1.32, wherein the largest angle θ_(NA) in theliquid 180 meets sin θ_(NA)=0.9, the liquid 180 has a refractive indexof 1.47, and the illumination system meets σ_(MAX)=0.9. The projectionexposure apparatus is a reduction projection exposure. While a targetpattern size and a mask pattern size are different according to thereduction ratio of the exposure apparatus. The following descriptionconverts a pattern size on the mask 130 into a size on the wafer 170.

FIGS. 11A and 11B show contrast depths (μm) while varying criticaldimensions and intervals, or pitches, in the mask pattern shown in FIG.2C which mixes line- and-space (“L/S”) patterns that have an equalcritical dimension and interval, and extend in the X and Y directions.

When sin θ_(NA)=0.9, θ_(NA) was 64°. Sin(90−θ_(NA))/sinθ_(NA)=0.44/0.9=0.49. Since a value of σ corresponding to a region uponwhich only the s-polarized light is incident along an axis parallel tothe pattern direction should meet 0.44/0.9≦σ≦σ_(MAX), the illuminationsystem should be designed so that the s-polarized light region isassigned to an area that meets about 0.5≦σ≦0.9.

FIG. 11A also shows contrast depths of focus(μm) for the illuminationcondition illustrated in FIG. 5D, in which a non-polarized circulareffective light source with σ of 0.5, and the tangentially polarizedregion between 0.5≦σ≦0.9 are realized and corresponds to theillumination “A” in FIG. 11A. It is compared with a non-polarizedcircular effective light source that meets σ_(MAX)=0.9 shown in FIG. 6and corresponds to the illumination “B” in FIG. 11A. The polarizationcontrol increases the depth of focus for fine critical dimensions,extending resolution limits, while that in large dimension does notchange greatly. It is thus confirmed that the depths of focus can beimproved for fine critical dimensions. The reduced contrast innon-polarization is a major problem in resolving fine patterns, but itis found that fine patterns can be resolved by using an effective lightsource that controls polarization.

FIG. 11B also shows contrast depths of focus(μm) for annularillumination that shields inside σ0.5 and has polarization in atangential direction shown in FIG. 9B that meets 0.5≦σ≦0.9 andcorresponds to the illumination “A” in FIG. 11B, which is to be comparedwith a non-polarized circular effective light source that meetsσ_(MAX)=0.9 shown in FIG. 6 and corresponds to the illumination “B” inFIG. 11B. Light shielding in a range of σ≦0.5 cuts low frequencycomponents inside the pupil in the optical system, and increases a depthfor fine critical dimensions without reducing depths for largedimensions, greatly extending resolution, limits. For patterning thefine patterns, the effect of s-polarized light is apparent.

EXAMPLE 2

A description will be given of an example 2 according to the presentinvention utilizing the immersion type exposure apparatus. Similar tothe example 1, this exposure apparatus uses ArF excimer laser (with awavelength of 193 nm) as the light source 112, and projection opticalsystem 140 having a numerical aperture of 1.32, wherein the largestangle θ_(NA) in the liquid 180 meets sin θ_(NA)=0.9, the liquid 180 hasa refractive index of 1.47, and the illumination system has σ_(MAX)=0.9.

FIGS. 12A and 12B show contrast depths of focus(μm) while varyingcritical dimensions and intervals, or pitches, in the unidirectionalmask pattern shown in FIG. 2A which includes L/S patterns that have anequal critical dimension and interval, and extend parallel to the Ydirections.

When sin θ_(NA)=0.9, θ_(NA) was 64°. sin (90−θ_(NA))/sinθ_(NA)=0.44/0.9=0.49. Since a value of σ corresponding to a region uponwhich only the s-polarized light is incident along the axis parallel tothe pattern direction should meet 0.44/0.9≦σ≦σ_(MAX), the illuminationsystem should be designed so that the s-polarized light region isassigned to an area that meets about 0.5≦σ≦0.9.

FIG. 12A also shows contrast depths of focus(μm) for polarization in atangential direction shown in FIG. 5D that meets 0.68≦σ≦0.9 andcorresponds to the illumination “A” in FIG. 12A, which is to be comparedwith a non-polarized circular effective light source that meetsσ_(MAX)=0.9 shown in FIG. 6 and corresponds to the illumination “B” inFIG. 12A. Control over the polarization increases a depth for finecritical dimensions, extending resolution limits, without reducingdepths for large critical dimensions, greatly extending resolutionlimits. A significant effect is available in case of such aunidirectional pattern. It is thus confirmed that the depths of focuscan be improved for fine critical dimensions. The reduced contrast innon-polarization is a major problem in resolving fine patterns, but itis clear that fine patterns can be resolved by using an effective lightsource that controls polarization.

The illumination “A” that includes polarized light in a tangentialdirection within a range of 0.68≦σ≦0.9 satisfies only part of predefinedcondition for the s-polarized light area, which requires polarized lightin a tangential direction within a range of 0.5≦σ≦0.9. Instead, it canbe said that no polarized light is used which is orthogonal to thetangential direction within a range of 0.5≦σ≦0.9. In other words, thecondition that requires polarized light in a tangential direction withina range of 0.5≦σ≦0.9 is replaced with the condition that eliminatespolarized light orthogonal to the tangential direction within a range of0.5≦σ≦0.9.

FIG. 12B also shows contrast depths (μm) for illumination shown in FIG.8C with 0.5≦σ≦0.9, and a tangential center point at X=0.7 and a radiusof 0.2 on a pupil coordinate system (corresponding to the illumination“A” in FIG. 12B), which is to be compared with a non-polarized circulareffective light source that meets σ_(MAX)=0.9 shown in FIG. 7 andcorresponds to the illumination “B” in FIG. 12B. Light shielding in arange of σ≦0.5 cuts low frequency components inside the pupil in theoptical system, and increases a depth for fine critical dimensionswithout reducing depths for large critical dimensions, greatly extendingresolution limits. When only the fine patterns exist, light except thes-polarized light can be shielded without problem. Almost the sameeffect is available even when the dipole illumination has a shape shownin FIG. 8A, 8B or 8 d, and a result thereof will be omitted. The reducedcontrast in non-polarization is a major problem in resolving finepatterns, but it is clear that fine patterns can be resolved by using aneffective light source that controls polarization.

While the present example discusses with NA=1.32, an effect of thisexposure method remarkably appears as NA is higher and as patternsbecome finer. The immersion optical system has a point where the imagingcontrast for p-polarized light becomes 0. This phenomenon significantlyreduces the depth of focus of the conventional exposure system.

While the present embodiment discusses polarization peculiar to theimmersion type projection optical system, the immersion has another bigproblem of fluctuations of the liquid 180 itself. While it is assumedthat the liquid 180 has a refractive index of n_(o), a lump may have arefractive index of n_(o)+Δn due to the fluctuations of temperature, forexample, as shown in FIG. 13. When the fluctuation occurs, the absolutevalue ΔW of the fluctuation of wave front aberration has the largestvalue expressed by the following Equation:ΔW=Δn·d/cos θ_(MAX)  (10)where d is a thickness of the immersion medium, and the followingEquation (11) is led from Equation (10):d≦(30mλ)·cos θ_(MAX) /Δn  (11)When a allowable amount of ΔW is 30 m λ, θ_(MAX)=60°, a wavelength is193 nm, Δn=10 ppm in Equation 11, d≦3000λ cos θ_(NA)=0.29 nm, a value ofattainable value. Only when d is small, influence of any fluctuation maybe reduced. Accordingly, it is important for the immersion exposuresystem to make d as small as possible.

Pure water is suitable for the liquid 180 for immersion exposure thatutilizes ArF excimer laser. However, among the elements in theprojection optical system 140, the last element, which is the closest tothe wafer 170, of the projection optical system 140 contacts the liquid180 that receives the largest optical energy. Therefore, quartz is notavailable due to the durability of a glass material, such as compaction,and calcium fluoride should be used. However, calcium fluoride hasdeliquescence and gets damaged when contacting water. A film for the ArFregion has conventionally been usually manufactured with evaporationmethod, but an evaporated film is so porous that calcium fluoride getsdamaged through holes. Accordingly, the present embodiment ischaracterized in using a sputtered film for a bottom surface of theprojection optical system 140 which contacts the liquid 180, protectingthe calcium fluoride substrate and achieving anti-reflection. Therefore,a sputtered film using, for example, MgF₂ is one of the suitablematerial for this purpose.

Referring to FIGS. 14 and 15, a description will now be given of anembodiment of a device fabricating method using the above exposureapparatus 100. FIG. 14 is a flowchart for explaining a fabrication ofdevices (i.e., semiconductor chips such as IC and LSI, LCDs, CCDs,etc.). Here, a description will be given of a fabrication of asemiconductor chip as an example. Step 1 (circuit design) designs asemiconductor device circuit. Step 2 (mask fabrication) forms a maskhaving a designed circuit pattern. Step 3 (wafer making) manufactures awafer using materials such as silicon. Step 4 (wafer process), which isreferred to as a pretreatment, forms actual circuitry on the waferthrough photolithography using the mask and wafer. Step 5 (assembly),which is also referred to as a post-treatment, forms into asemiconductor chip the wafer formed in Step 4 and includes an assemblystep (e.g., dicing, bonding), a packaging step (chip sealing), and thelike. Step 6 (inspection) performs various tests for the semiconductordevice made in Step 5, such as a validity test and a durability test.Through these steps, a semiconductor device is finished and shipped(Step 7).

FIG. 15 is a detailed flowchart of the wafer process in Step 4. Step 11(oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ion into the wafer. Step 15 (resist process)applies a photosensitive material onto the wafer. Step 16 (exposure)uses the exposure apparatus 100 to expose a circuit pattern on the maskonto the wafer. Step 17 (development) develops the exposed wafer. Step18 (etching) etches parts other than a developed resist image. Step 19(resist stripping) removes disused resist after etching. These steps arerepeated, and multilayer circuit patterns are formed on the wafer. Thedevice manufacture method of the present invention may manufacturehigher quality devices than the conventional one. Thus, the devicemanufacture method using the inventive lithography, and resultantdevices themselves as intermediate and finished products also constituteone aspect of the present invention. Such devices include semiconductorchips like an LSI and VLSI, CCDs, LCDs, magnetic sensors, thin filmmagnetic heads, and the like.

Thus, the present invention can provide an immersion type exposuremethod and apparatus which prevent deteriorated imaging performance dueto influence of polarization, maintain desired contrast, and form adesired pattern.

Further, the present invention is not limited to these preferredembodiments, and various modifications and changes may be made in thepresent invention without departing from the spirit and scope thereof.

1. An exposure method for transferring a pattern formed on a mask ontoan object to be exposed, said method comprising: directing exposurelight having a wavelength λ (nm) through a projection optical systemthat is at least partially immersed in liquid and has a numericalaperture of n_(o)·sin θ_(NA) greater than 0.9 in order to transfer apattern formed on a mask onto an object to be exposed; wherein n_(o) isa refractive index of the liquid, Δn is a fluctuation of refractiveindex of the liquid, θ_(NA) is the largest angle common to the liquidand a resist material applied to the object to be exposed, and d is athickness of the liquid in an optical-axis direction of the projectionoptical system which satisfies d ≦(0.03λ)cosθ_(NA)/Δn.